This invention relates to a method of providing a structure made primarily of ice at a desired location and more particularly relates to a method of transporting an offshore ice structure from a first frigid area where it is constructed to another frigid area where said structure is to be used.
In producing hydrocarbons from hostile, frigid environments, e.g., Arctic shelf, many problems are encountered which are not normally present in other offshore areas. These problems arise from the ever-changing ice conditions in these areas. For example, in winter "fast ice" may attach itself to shore and extend outward as much as 50 miles in places. Such ice could serve as a temporary, stable platform for drilling or other operations but, unfortunately, this ice breaks up during the thawing period and "shore-leads" of open water develop through the ice. While the leads are open, floating drilling operations might be carried out but the risk is great since pack ice frequently moves shoreward under the influence of winds and currents. When this happens, the pack ice can completely close the shore-leads, thereby damaging any equipment within the leads. Further, this pack ice, which may range up to ten feet or more in thickness, can exert massive force which may be too great to be resisted by any practical drilling/production fixed platform of the conventional type. Therefore, to operate successfully in these areas, any drilling/production structure must be capable of withstanding or avoiding the force of the moving pack ice.
One structure which can successfully resist such forces is an island which extends upward from an anchored position on the marine bottom to a distance above the waterline. Ideally, this island would be a naturally occurring one but unfortunately such islands are not normally present in this area or are located in the wrong places to serve a particular field. It follows that in most instances if an island is to be used, it must be of some other form.
At least three alternate forms of such islands have been proposed: (1) artificial islands built of earth materials and the like; (2) natural ice islands; and (3) artificial ice islands. As to artificial earth islands, the severe shortage or difficulty of obtaining the required materials in the Arctic areas makes their use impractical in most of these areas. The use of natural ice islands in these areas has been investigated as reported in OIL AND GAS JOURNAL, July 28, 1969, pp. 118-119, but these attempts were abandoned due to severe cracking of the islands. A further difficulty is that natural ice islands are unlikely to be present at the desired location and time. This leaves artificial ice islands to which the present invention relates.
In U.S. Pat. No. 3,750,412, issued Aug. 7, 1973, there is fully described a method of constructing an artificial ice island by utilizing the naturally occurring freezing temperatures found in certain frigid areas. An ice floe or a portion of fast ice is selected as a base on which ice is accumulated by freezing water which is sprayed or flooded onto said base. The base under the added weight of the accumulated ice will begin to sink toward the marine bottom. Accumulation of ice is continued until the structure attains a desired thickness.
The areas having the extreme temperatures necessary for the rapid freezing of water to form such structures, however, are not always the same areas as those where said structures are ultimately to be used. Furthermore, in some areas where such structures are to be used, movement of pack ice is such that it is virtually impossible to anchor an ice floe or the like over an exact location and maintain that position while an island is being constructed. Therefore, for use of such structures to be practical, there is a need for a method of constructing an ice structure in an area best suited for this purpose and then economically transporting it to the location where it is to be used.